We propose to continue studies defining the electrical fields generated by chronic and transient myocardial ischemia. Four projects are defined. First, the equivalent generator properties of the isolated canine heart will be determined before and after coronary ligation. Efforts will be focused on determining the physiologic relevance of dipole ranging methods in assessing the location and extent of ischemic lesions. Second, isopotential mapping and dipole ranging techniques will be applied to surface recordings from intact dogs before and after coronary occlusion to extend the results from isolated hearts to intact animal models. Third, human subjects with acute myocardial infarction will be investigated to determine the patterns of ST-T abnormalities in relation to lead system design, equivalent generator properties and electrogenesis of standard ECG abnormalities. Last, surface mapping during supine exercise will continue in an effort to define the relation between coronary pathoanatomy and distribution of ECG changes, to evaluate lead system design, and to determine diagnostic criteria in subjects with abnormal resting electrocardiograms.